March ao, 1882] NATURE 513 
the mouth of the discharge-pipe. The cap being blown | some of the strings might be broken, opening the dis- 
off, the air escapes, and thus, by the arrangements already | charge-cocks, and thus flooding the men employed, and 
described, the water discharges by the opening made by | causing a false alarm and useless waste. That objection 
the explosion. This string-arrangement, however, is not | is entirely avoided by the electric system. 
free from objections. In scene-shifting, for example, Electric System —In this self-acting extinguishing ap- 
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Fic. 4.—Arrangement cf system of pipes above and below the stage. 
paratus, the network of pipes is the same as in the | temperature caused by the fire ; (2) a self-acting supply- 
mechanical system, but they are not filled with com- | cock, to send water into the system of pipes from the 
pressed air. The system, as a whole, is composed of main pipe in the street; (3) an arrangement for opening 
three distinct parts :—(1) an apparatus which completes the discharge-pipes upon any part which is in danger. 
the electric circuit, under the action of the raising of The apparatus (1) for completing the electric circuit is 
